A turboprop with two propellers is known, e.g. from U.S. Pat. No. 4,758,129, which turboprop comprises a turbine with two contrarotating rotors driving respective ones of the two propellers, each of which is formed by a set of variable-pitch blades. The invention applies in particular to that type of airplane turboprop. Furthermore, various blade pitch control mechanisms are known. For example, one known system comprises a conventional actuator disposed axially in the inside space formed at the center of the annular-flowpath turbine. Mechanical connections transmit the movement of the actuator rod radially to the variable-pitch blades.
Those connection elements are complex, bulky, heavy, and expensive. Furthermore, a single actuator is required to provide the forces that need to be transmitted in order to vary the pitch of all of the blades in a given set, thereby requiring high actuator pressures for the actuator, given that the piston of such an axially-installed actuator necessarily presents an area that is small. This high control pressure is prejudicial to the actuator possessing a long lifetime.
In addition, maintenance is made complicated since the vital elements are situated inside the casing, and more particularly, in some cases, inside the turbine. They cannot be changed without dismantling the turbine.
The invention seeks to overcome those drawbacks.